At least some Amazon.com visitors experienced a curious glitch of some kind. According to @mit429, @LeighEllwood, @vagari, @WeberBooks -- to name a few, Amazon showed some or all titles as "unavailable." According to @Chris_Rotella, when he phoned Amazon (you can do that?), they told him that systems were being "updated" at the time.
According to the Twitter timestamps, the problem occurred sometime after 11A Eastern.
The Amazon AWS status page reported an ECS power failure that affected certain instances running in a specific affected server rack, but that had been remedied by 1:20A PDT. I don't know whether Amazon proper is running on the Amazon Web Services infrastructure, (despite use of the inset AWS image) but it may not be coincidental. The buzz would have been much larger if all of Amazon everywhere had been affected.